1. Field of the Invention
The present invention relates to a piercing apparatus for making a hole in a workpiece by engagement of a pair of rotary rollers.
2. Description of the Related Art
In conventional pressing machines, as piercing apparatuses, to make holes in a workpiece, for example, the workpiece in the form of an elongated thin sheet whose length is much greater than the thickness thereof is moved in the lengthwise direction thereof and is introduced in a press die to form elongated holes elongated in the lengthwise direction or the width direction thereof.
In known press machines, upon pressing, such as precision shearing, it is necessary to temporarily stop the feed of the thin sheet and move the upper and lower dies close to each other to pierce the thin sheet, while holding the periphery of the thin sheet. To this end, the feed speed and the stopping position of the thin sheet must be accurately controlled. However, the higher the piercing speed, the lower the accuracy, and hence it is difficult to increase the speed of the piercing of the thin sheet.
Moreover, to increase the piercing speed for the thin sheet, it is necessary to provide a chip discharge apparatus which can immediately and effectively discharge chips cut away from the thin sheet. However, the chips which are produced when elongated holes whose length in the lengthwise direction of the thin sheet is much longer than the thickness of the thin sheet are formed can twine around each other or the discharge passageway may be blocked with the chips. If this occurs, the press machine must be stopped at each occurrence to remove the entwined chips, thus making it difficult to increase the piercing speed of the thin sheet.
In recent years, there has been a need to carry out the press process of a workpiece and the mounting process of the workpiece thus machined in the same process line. To this end, it has been proposed to incorporate the press process in the mounting process. However, since the pressing speed, of the workpiece, by the press machine is low in comparison with the mounting speed which has been increased in an automated production line, it is necessary to reduce the mounting speed so as to meet the lower press speed. Under these circumstances, it required to provide a press machine having a high press speed corresponding to the mounting speed.